Crustal architecture and tectonic assembly of the Central Gneiss Belt, southwestern Grenville Province, Canada: a new interpretation

2000 ◽  
Vol 37 (2-3) ◽  
pp. 217-234 ◽  
Author(s):  
J WF Ketchum ◽  
A Davidson
Keyword(s):  
Structural Model ◽  
Hanging Wall ◽  
Mafic Rock ◽  
Grenville Province ◽  
The North ◽  
Rock Types ◽  
Structural Barrier ◽  
New Interpretation ◽  
Central Gneiss Belt ◽  
Tectonic Boundary

The Central Gneiss Belt, southwestern Grenville Province, is characterized by parautochthonous crust in the north and allochthonous lithotectonic domains in the south. Despite nearly two decades of study, the basal décollement to allochthonous domains transported from the southeast, known as the allochthon boundary thrust, has not been precisely located throughout much of the belt. Between Lake Nipissing and Georgian Bay where its surface trace is known, it separates 1.24 Ga Sudbury metadiabase in the footwall from eclogite remnants and 1.17-1.15 Ga coronitic olivine metagabbro confined to its hanging wall. On the premise that this relationship can be used to trace the allochthon boundary thrust elsewhere in the Central Gneiss Belt, we have sought to extend the known distribution of these mafic rock types, making use of field, petrographic, and geochemical criteria to identify them. New occurrences of all three mafic types are identified in a region extending from south of Lake Nipissing to western Quebec, and the mutually exclusive pattern of occurrence is maintained within this region. Structural trends and reconnaissance mapping of high-strain zones that appear to represent a structural barrier to the mafic suites suggest that the allochthon boundary thrust lies well to the north of its previously suggested location. Our preferred surface trace for it passes around the southern end of the Powassan batholith and through the town of North Bay before turning east to join up with the Lac Watson shear zone in western Quebec. This suggests that a large segment of "parautochthonous" crust lying north of, and including, the Algonquin domain is in fact allochthonous. The mutually exclusive distribution of the mafic suites points to significant separation of allochthonous and parautochthonous components prior to the Grenvillian orogeny, in accord with models of pre-Grenvillian continental rifting proposed by others. Despite a relative abundance of geological and geochronological data for the Central Gneiss Belt and a mafic rock distribution that appears to successfully locate a major tectonic boundary, we emphasize the need for additional field and laboratory work aimed at testing our structural model.

Pre-Grenvillian and Grenvillian lithotectonic regions in eastern Labrador—correlations with the Sveconorwegian Orogenic Belt in Sweden

1984 ◽  
Vol 21 (6) ◽  
pp. 678-693 ◽  
Author(s):  
Charles F. Gower ◽  
Victor Owen
Keyword(s):  
Orogenic Belt ◽  
Grenville Province ◽  
Pluton Emplacement ◽  
Mafic Intrusions ◽  
The North ◽  
Rock Types ◽  
Structural Style ◽  
Opening And Closing ◽  
Layered Mafic Intrusions ◽  
Middle Proterozoic

The Trans-Labrador batholith, Groswater Bay Terrane, and Lake Melville Terrane are three major crustal segments located adjacent to or within the Grenville Province in eastern Labrador. Each crustal segment is a distinct lithotectonic entity displaying contrasts with each other in proportions of rock types, structural style, and metamorphic imprint. Together they indicate a unilateral polarity to the region, partly reflecting Grenvillian tectonism, which sliced the region into thrust-bound blocks.In all three crustal segments, an Archean or Aphebian gneissic basement is inferred onto or adjacent to which ca. 1900–1700 Ma supracrustal rocks were deposited. Deformation, metamorphism, and granitoid pluton emplacement were partly coeval with and partly postdated the supracrustal assemblages. In the north, tectonothermal effects can be assigned to Hudsonian–Ketilidian orogenesis but their peak was 50–100 Ma later farther south. Post-tectonic granitoid plutons and layered mafic intrusions were emplaced at about 1650–1600 Ma, and further pulses of mafic intrusion occurred prior to the Grenvillian Orogeny.Comparison with the Sveconorwegian Orogenic Belt in southern Sweden shows remarkable similarities in lithologies, geological histories, and structural style. The Småland–Värmland granitoid belt, Eastern Pregothian mega-unit, and Western Pregothian mega-unit are interpreted here to be the Scandinavian counterparts of the Trans-Labrador batholith, Groswater Bay Terrane, and Lake Melville Terrane, respectively. This correlation is taken to indicate that both regions were part of the same tectonic margin during Middle Proterozoic times.The implication of this correlation is that the opening and closing of the lapetus Ocean resulted in a 2000 km sinistral "offset" of the Grenvillian–Sveconorwegian Front and other Precambrian features on either side of the Caledonides suture.

Nd isotope mapping of the Allochthon Boundary Thrust on the shores of Georgian Bay, Ontario: significance for Grenvillian crustal structure and evolution

2015 ◽  
Vol 152 (6) ◽  
pp. 993-1008 ◽  
Author(s):  
ALAN DICKIN ◽  
ROBERT NORTH
Keyword(s):  
Crustal Structure ◽  
Large Scale ◽  
Geological Mapping ◽  
Grenville Province ◽  
Nd Isotope ◽  
Georgian Bay ◽  
Lithological Mapping ◽  
Depleted Mantle ◽  
Central Gneiss Belt ◽  
Tectonic Boundary

AbstractNearly 50 new Nd isotope analyses are presented for the Shawanaga region of Georgian Bay, Ontario, to study crustal evolution in the Grenvillian Central Gneiss Belt. Depleted mantle (TDM) Nd model ages are used to map a major Grenvillian tectonic boundary, the Allochthon Boundary Thrust (ABT), which in the Shawanaga area separates gneisses with TDM ages above and below 1.65 Ga. This is lower than the 1.8 Ga age cut-off observed further north, and is attributed to a southward increase in Mesoproterozoic magmatic reworking of an original Palaeoproterozoic continental margin, causing a progressive southward decrease in Nd model ages. Between Shawanaga Island and Franklin Island, Nd isotope mapping yields an ABT trajectory that closely matches published geological mapping, and passes within 100 m of four retrogressed eclogite bodies typically associated with the thrust boundary. This validation of the method gives confidence in the mapped trajectory south of Snake Island, where sparse outcrop inhibits lithological mapping. The new results suggest that published 1.7–1.9 Ga TDM ages in the Lower Go Home domain of the Central Gneiss Belt further south are also indicative of parautochthonous crust. Hence, we propose that the main ramp of the ABT is located in the immediate hangingwall of the Go Home domain, much further south than generally recognized. This has important implications for the large-scale crustal structure of the SW Grenville Province, suggesting that the ABT ramp has a similar curved trajectory to the Grenville Front and the Central Metasedimentary Belt boundary thrust.

Paleoproterozoic crustal history of the southwestern Grenville Province: evidence from Nd isotopic mapping

1995 ◽  
Vol 32 (4) ◽  
pp. 472-485 ◽  
Author(s):  
C. Holmden ◽  
A. P. Dickin
Keyword(s):  
Crustal Material ◽  
Grenville Province ◽  
Detrital Zircon Geochronology ◽  
Bay Area ◽  
The North ◽  
History Of ◽  
Depositional Age ◽  
Central Gneiss Belt ◽  
Superior Craton ◽  
Common Association

Nd isotopic mapping in the North Bay area of the Central Gneiss Belt, southwestern Grenville Province, has revealed the precise trend of a TDM model age line developed between the uplifted southern margin of the Archean Superior craton (TDM = 2.7 Ga) and a Paleoproterozoic allochthon (TDM = 1.9 Ga). Separating these two crustal blocks is a narrow zone of gneisses with intermediate TDM ages. These transitional gneisses are interpreted to reflect a remnant fault or ductile shear zone, of uncertain age, along which crustal material from both blocks mechanically mixed during their juxtaposition. Accordingly, the nature of the TDM line in the North Bay area is interpreted to be tectonic. In the Temiscaming area, widespread exposures of mature metasedimentary gneisses are shown by their TDM ages to be dominantly of Paleoproterozoic provenance. These results are consistent with the existing detrital zircon geochronology, inferring a maximum depositional age of ~1.7 Ga. The anorogenic chemistry of the North Bay orthogneiss and mixed calc-alkaline–alkaline chemistry of the Temiscaming gneisses suggest a connection between Paleoproterozoic anorogenic magmatism and synsedimentary quartzite deposition, which is a common association in 1.9–1.6 Ga accretionary orogens of southern Laurentia. The relatively close correspondence between widespread 1.9 Ga TDM ages and U–Pb crystallization ages as old as 1.74 Ga implies that rocks of the Central Gneiss Belt were originally the juvenile products of Paleoproterozoic orogenesis.

Late Labradorian metamorphism and anorthosite–granitoid intrusion, Cape Caribou River allochthon, Grenville Province, Labrador: evidence from U–Pb geochronology

1995 ◽  
Vol 32 (9) ◽  
pp. 1411-1425 ◽  
Author(s):  
François Bussy ◽  
Thomas E. Krogh ◽  
Richard J. Wardle
Keyword(s):  
Hanging Wall ◽  
Granulite Facies ◽  
Grenville Province ◽  
Mafic Dykes ◽  
North West ◽  
The North ◽  
Form Part ◽  
Thrust System ◽  
Granitoid Gneisses ◽  
New Generation

In the Cape Caribou River allochthon (CCRA), metaigneous and gneissic units occur as a shallowly plunging synform in the hanging wall of the Grand Lake thrust system (GLTS), a Grenvillian structure that forms the boundary between the Mealy Mountains and Groswater Bay terranes. The layered rocks of the CCRA are cut by a stockwork of monzonite dykes related to the Dome Mountain suite and by metadiabase–amphibolite dykes that probably form part of the ca. 1380 Ma Mealy swarm. The mafic dykes appear to postdate much of the development of subhorizontal metamorphic layering within the lower parts of the CCRA. The uppermost (least metamorphosed) units of the CCRA, the North West River anorthosite–metagabbro and the Dome Mountain monzonite suite, have been dated at 1625 ± 6 and 1626 ± 2 Ma, respectively. An amphibolite unit that concordantly underlies the anorthosite–metagabbro and is intruded discordantly by monzonite dykes has given metamorphic ages of 1660 ± 3 and 1631 ± 2 Ma. Granitoid gneisses that form the lowest level of the CCRA have given a migmatization age of 1622 ± 6 Ma. The effects of Grenvillian metamorphism become apparent in the lower levels of the allochthon where gneisses, amphibolite, and mafic dykes have given new generation zircon ages of 1008 ± 2, 1012 ± 3, and 1011 ± 3 Ma, respectively. A posttectonic pegmatite has also given zircon and monazite ages of [Formula: see text] and 1013 ± 3 Ma, respectively. Although these results indicate new growth of Grenvillian zircon, this process was generally not accompanied by penetrative deformation or melting. Thus, the formation of gneissic fabrics and the overall layered nature of the lower CCRA are a result primarily of Labradorian (1660–1620 Ma) tectonism and intrusion, and probably reflect early movement on an ancestral GLTS. Grenvillian heating and metamorphism (up to granulite facies) was strongly concentrated towards the base of the CCRA and probably occurred during northwestward thrusting of the allochthon over the Groswater Bay terrane.

Lithostratigraphy of the Copperton Formation, Areachap Group

2019 ◽  
Vol 122 (4) ◽  
pp. 561-570
Author(s):  
D.H. Cornell
Keyword(s):  
Hanging Wall ◽  
Shear Zones ◽  
Massive Sulphide ◽  
Sulphide Deposit ◽  
Continental Scale ◽  
The North ◽  
Rock Types ◽  
Wide Range ◽  
Copper Mines ◽  
Silicate Rocks

Abstract The type area of the Copperton Formation is on the farms Vogelstruisbult 104, Somuspan 105 and Dooniespan 108 in Prieska District. Outcrop is poor and the type material is preserved in exploration borehole cores from the Prieska Copper Mines and the Annex Cu-Zn deposits. It is highly deformed and variably metamorphosed. Thus it is a lithodemic unit, but interpreted as a supracrustal sequence and described as a formation including lithologically distinct members. The Copperton Formation comprises a wide range of rock types including metabasic and intermediate gneisses with minor amounts of metapelitic and calc-silicate rocks. Metamorphic parageneses generally reflect amphibolite facies metamorphism, but granulite and retrograde greenschist facies zones also occur. The protoliths are interpreted as an arc-related volcano-sedimentary package and the Smouspan Member metadacite is dated at 1284 ± 9 Ma. Members are distinguished as follows: The Magazine Member is dominated by calc-silicate rocks which are dominant in outcrop but rarely found in borehole cores. The Smouspan Gneiss is a fairly homogeneous hornblende-biotite intermediate gneiss which is up to 400 meters thick in an isoclinal fold structure. It comprises the footwall to the Prieska Copper Mines Member, in which the massive sulphide orebody occurs, enclosed in an alteration assemblage comprising dark gedrite fels and strongly foliated, leucocratic quartz-perthite-sillimanite gneiss. The ore is interpreted as a volcanogenic massive sulphide deposit formed in a Mesoproterozoic island arc system. The Vogelstruisbult Member is the hanging wall unit, comprising mainly laminated amphibolites and metapelites, but also containing a variety of rock types including hornblende gneiss, biotite gneiss, chlorite schist, and calc-silicate gneiss. Away from the Prieska Mines orebody, a similar variety of rock types is found, and not subdivided but classified as Copperton Formation, a mappable unit. The same assemblage of rock types, including massive sulphide mineralization, was intersected in drill holes on the farms Kielder (portion of Doonies Pan 108), Eierdop Pan and Kantienpan to the north. The Copperton Formation is the southernmost unit of the Areachap Group which is exposed between Prieska Copper Mines and Areachap Mine north of Upington, where the Jannelsepan and Bethesda formations occur. The Copperton Formation is partly obscured in many places by Dwyka Group tillite cover which thickens southwards. A sequence of structural and metamorphic events affected the Copperton Formation and Areachap Group during the 1.2 to 1.0 Ga Namaqua-Natal orogeny. These involved collision of the Areachap Terrane with the Kaapvaal-Rehoboth Craton at about 1220 Ma, a thermal and deformational event coeval with the continental-scale Umkondo mantle event at about 1100 Ma, followed by uplift, erosion and the development of right-lateral shear zones of the Doornberg Lineament, with cooling below 300°C by 920 Ma. A Cambrian peneplain developed in the region which was first covered by Nama Group sandstones, then glaciated and covered by Permian Dwyka Group tillites which are presently being eroded to expose the Copperton Formation.

MODEL OF THE NORTH CAUCASIAN FEDERAL DISTRICT FOOD MARKETS SPATIAL ORGANIZATION

1970 ◽  
pp. 4-9
Author(s):  
А. Kh. Dikinov ◽  
А. А. Eshugaova ◽  
М. М. Abdurakhmanova ◽  
М. А. Sadueva
Keyword(s):  
Economic Development ◽  
Spatial Organization ◽  
Structural Model ◽  
Research Evaluation ◽  
Federal District ◽  
North Caucasus ◽  
Food Markets ◽  
Regional Food ◽  
The North ◽  
Food Market

The most progressive and promising model of spatial organization of food markets of the North Caucasus Russian Theatre is a cluster model. In the proposed methodology of the process approach to develop a structural model of agro-food cluster in the NORTH is cluster analysis. The regional food market as a single system, which combines production, marketing and consumption of foods with a specific hierarchy, is characterized by different relationships and proportions between its components and is an important an indicator of a country's economic development, achieving food security. Disclosure of potential in a market system, its effective use, taking into account regional particularities and specificities of the economy, improvement of the spatial organization and improving the efficiency of such a complex system as the regional food market is impossible without knowledge of its essence, principles of formation and operation. In this connection there was a need to develop modern methods of research, evaluation, analysis, improvement of structure and functional organisation of the regional food markets as an important factor for the socio-economic development the country. The novelty of the research lies in the fact that the clustering of agribusiness implemented taking into account the peculiarities of regional AIC on the basis of strategic management zones: industrial, conventional and organic. To determine the effectiveness of the cluster algorithm of its evaluation, which is based on the criteria of usefulness and survival in the conditions of the cluster in the region, which are defined using evaluation scales and weights the main factors utility and survival in the cluster.

The Metasomatized Mantle beneath the North Atlantic Craton: Insights from Peridotite Xenoliths of the Chidliak Kimberlite Province (NE Canada)

2019 ◽  
Vol 60 (10) ◽  
pp. 1991-2024 ◽  
Author(s):  
M G Kopylova ◽  
E Tso ◽  
F Ma ◽  
J Liu ◽  
D G Pearson
Keyword(s):  
North Atlantic ◽  
Thermal State ◽  
Mineral Chemistry ◽  
Mantle Metasomatism ◽  
Labrador Sea ◽  
The North ◽  
Rock Types ◽  
History Of ◽  
The North Atlantic ◽  
North Atlantic Craton

Abstract We studied the petrography, mineralogy, thermobarometry and whole-rock chemistry of 120 peridotite and pyroxenite xenoliths collected from the 156–138 Ma Chidliak kimberlite province (Southern Baffin Island). Xenoliths from pipes CH-1, -6, -7 and -44 are divided into two garnet-bearing series, dunites–harzburgites–lherzolites and wehrlites–olivine pyroxenites. Both series show widely varying textures, from coarse to sheared, and textures of late formation of garnet and clinopyroxene. Some samples from the lherzolite series may contain spinel, whereas wehrlites may contain ilmenite. In CH-6, rare coarse samples of the lherzolite and wehrlite series were derived from P = 2·8 to 5·6 GPa, whereas predominant sheared and coarse samples of the lherzolite series coexist at P = 5·6–7·5 GPa. Kimberlites CH-1, -7, -44 sample mainly the deeper mantle, at P = 5·0–7·5 GPa, represented by coarse and sheared lherzolite and wehrlite series. The bulk of the pressure–temperature arrays defines a thermal state compatible with 35–39 mW m–2 surface heat flow, but a significant thermal disequilibrium was evident in the large isobaric thermal scatter, especially at depth, and in the low thermal gradients uncharacteristic of conduction. The whole-rock Si and Mg contents of the Chidliak xenoliths and their mineral chemistry reflect initial high levels of melt depletion typical of cratonic mantle and subsequent refertilization in Ca and Al. Unlike the more orthopyroxene-rich mantle of many other cratons, the Chidliak mantle is rich (∼83 vol%) in forsteritic olivine. We assign this to silicate–carbonate metasomatism, which triggered wehrlitization of the mantle. The Chidliak mantle resembles the Greenlandic part of the North Atlantic Craton, suggesting the former contiguous nature of their lithosphere before subsequent rifting into separate continental fragments. Another, more recent type of mantle metasomatism, which affected the Chidliak mantle, is characterized by elevated Ti in pyroxenes and garnet typical of all rock types from CH-1, -7 and -44. These metasomatic samples are largely absent from the CH-6 xenolith suite. The Ti imprint is most intense in xenoliths derived from depths equivalent to 5·5–6·5 GPa where it is associated with higher strain, the presence of sheared samples of the lherzolite series and higher temperatures varying isobarically by up to 200 °C. The horizontal scale of the thermal-metasomatic imprint is more ambiguous and could be as regional as tens of kilometers or as local as <1 km. The time-scale of this metasomatism relates to a conductive length-scale and could be as short as <1 Myr, shortly predating kimberlite formation. A complex protracted metasomatic history of the North Atlantic Craton reconstructed from Chidliak xenoliths matches emplacement patterns of deep CO2-rich and Ti-rich magmatism around the Labrador Sea prior to the craton rifting. The metasomatism may have played a pivotal role in thinning the North Atlantic Craton lithosphere adjacent to the Labrador Sea from ∼240 km in the Jurassic to ∼65 km in the Paleogene.

scholarly journals Monazite U–Th–Pb geochronology of the Central Metasedimentary Belt Boundary Zone (CMBbz), Grenville Province, Ontario Canada

2018 ◽  
Vol 55 (9) ◽  
pp. 1063-1078 ◽  
Author(s):  
Michelle J. Markley ◽  
Steven R. Dunn ◽  
Michael J. Jercinovic ◽  
William H. Peck ◽  
Michael L. Williams
Keyword(s):  
Shear Zone ◽  
Crustal Thickening ◽  
Boundary Zone ◽  
Grenville Province ◽  
Metamorphic History ◽  
Crustal Thinning ◽  
Tectonic Significance ◽  
History Of ◽  
Central Gneiss Belt ◽  
Scale Shear

The Central Metasedimentary Belt boundary zone (CMBbz) is a crustal-scale shear zone that juxtaposes the Central Gneiss Belt and the Central Metasedimentary Belt of the Grenville Province. Geochronological work on the timing of deformation and metamorphism in the CMBbz is ambiguous, and the questions that motivate our study are: how many episodes of shear zone activity did the CMBbz experience, and what is the tectonic significance of each episode? We present electron microprobe data from monazite (the U–Th–Pb chemical method) to directly date deformation and metamorphism recorded in five garnet–biotite gneiss samples collected from three localities of the CMBbz of Ontario (West Guilford, Fishtail Lake, and Killaloe). All three localities yield youngest monazite dates ca. 1045 Ma; most of the monazite domains that yield these dates are high-Y rims. In comparison with this common late Ottawan history, the earlier history of the three CMBbz localities is less clearly shared. The West Guilford samples have monazite grain cores that show older high-Y domains and younger low-Y domains; these cores yield a prograde early Ottawan (1100–1075 Ma) history. The Killaloe samples yield a well-defined prograde, pre- to early Shawinigan history (i.e., 1220–1160 Ma) in addition to some evidence for a second early Ottawan event. In other words, the answers to our research questions are: three events; a Shawinigan event possibly associated with crustal thickening, an Ottawan event possibly associated with another round of crustal thickening, and a late Ottawan event that resists simple interpretation in terms of metamorphic history but that coincides chronologically with crustal thinning at the base of an orogenic lid.

scholarly journals Volcanic centres between Frigg Fjord and Midtkap, eastern North Greenland

1981 ◽  
Vol 106 ◽  
pp. 69-75
Author(s):  
I Parsons
Keyword(s):  
Fault Zone ◽  
Fold Belt ◽  
The South ◽  
The North ◽  
Rock Types ◽  
South West ◽  
North Greenland

A series of smal! volcanic centres cut Ordovician turbidites of Formation A in the southem part of Johannes V. Jensen Land between Midtkap and Frigg Fjord (Map 2). Their general location and main rock types were described by Soper et al. (1980) and their nomenclature is adopted here for fig. 22 with the addition of the small pipe B2. A further small intrusion, south-west of Frigg Fjord, was described by Pedersen (1980). The centres lie 5-10 km south of, and parallel to, the important Harder Fjord fault zone (fig. 22) which traverses the southern part of the North Greenland fold belt and shows substantial downthrow to the south (Higgins et al., this report).

scholarly journals Investigations of detrital zircon, rutile and titanite from present-day Labrador drainage basins: fingerprinting the Grenvillean front

1969 ◽  
pp. 77-80
Author(s):  
Tonny B. Thomsen ◽  
Christian Knudsen ◽  
Alana M. Hinchey
Keyword(s):  
Newfoundland And Labrador ◽  
Sedimentary Basins ◽  
Geological Survey ◽  
Drainage Basins ◽  
Grenville Province ◽  
Collaborative Project ◽  
North West ◽  
North East ◽  
The North ◽  
Three Samples

A multidisciplinary provenance study was conducted on stream sediment samples from major rivers in the eastern part of Labrador, Canada (Fig. 1). Th e purpose was to fi ngerprint the sources that deliver material to the stream sediments and to the reservoir sand units deposited off shore in the sedimentary basins in the Labrador Sea. We used a multimineral U-Pb geochronological approach employing rutile and titanite in addition to zircon to obtain unbiased age data. Th e purpose of this was to characterise the diff erent igneous and metamorphic episodes that occurred in Labrador, which is an area with highly variable geology characterised by the Palaeoproterozoic south-eastern Churchill province in the north-west, the Archaean Nain plutonic suite in the north-east, the Palaeoproterozoic Makkovik province in the east and the Mesoproterozoic Grenville Province to the south. Th e fi eld work was carried out in 2012 and 2013 and the study is a collaborative project between the Geological Survey of Denmark and Greenland and the Geological Survey of Newfoundland and Labrador. In this paper we focus on three samples from the southern part of the study area where two parts of the Grenville orogeny are found (Fig. 1).

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